Method and Apparatus for Forming a Remote Beam

ABSTRACT

A device and method are provided for forming a beam of a transmit antenna array in the direction of a positioning receiver. Since the beam of the transmit antenna array is formed remotely by the positioning receiver, the received gain of the incoming positioning signal is maximised while signals from other directions are attenuated, thereby mitigating any unwanted effects of multipath. Depending on the number of elements in the transmit antenna array and their physical distribution, the width of the beam can be made finer such that the positioning receiver only requires a simple omni-directional antenna to achieve an accurate positioning solution.

FIELD OF THE INVENTION

The present invention relates generally to positioning systems and inparticular to subsystems for receiving positioning signals.

The invention has been developed primarily for forming remote beams forreceiving positioning signals in multipath environments and will bedescribed hereinafter with reference to this application. However, itwill be appreciated that the invention is not limited to this particularfield of use.

BACKGROUND OF THE INVENTION

Any discussion of the prior art throughout the specification should inno way be considered as an admission that such prior art is widely knownor forms part of the common general knowledge in the field.

As is known in the art, positioning technologies generally operate bymeasuring the time a signal takes to traverse from a signal source tothe receiving device. In most prior art applications, this measurementis taken by comparing the time at which a signal is sent with the timeat which the same signal is received. Common positioning systems such asGPS use three or more such signals and, using trilateration, calculatean object's position. Since the measurement calculations aretime-sensitive, a fourth signal is commonly required to ensure that theclocks of the source and the receiver are properly synchronised.

Multipath refers to the phenomenon whereby positioning signals arereflected off other objects, such as walls and furniture. This isespecially prevalent in an enclosed environment, such as indoors, but isalso a significant problem in built up areas, such as in cities.Simplistically speaking, reflected signals take longer to traverse froma source to a receiver, therefore affecting the accuracy of themeasurements. Also the receiver sees conflicting signals originatingfrom the same source, having different timing information. Some modernreceivers use selection algorithms to try to determine the mostappropriate signal to use in position determination. However, receiverstypically cannot differentiate multipath signals from the genuinepositioning signals to any high degree of accuracy.

Also known in the art are phased arrays, consisting of a number ofantenna elements that can be individually controlled to direct a beam.In a typical phased array, signals received at each element areindividually phase and gain manipulated, the exact manipulation requireddepending on the direction of the beam required. The resulting phase andgain manipulated signals from each element are then summed to obtain thedesired direction of the beam.

One method for mitigating the problem of multipath is discussed inpublished international patent application WO 2011/000049 A1 which isassigned to the present applicant and hereby incorporated in itsentirety by reference. This application discusses a method to form abeam using a local receiver antenna to receive a positioning signal froma transmission source, thereby ignoring other signals in a multipathenvironment.

While this method is successful in mitigating the effects of multipath,the local receiver antenna necessarily requires a number of physicalantenna elements. This limits the size to which the local receiverantenna can be miniaturised, and therefore limits the portability of thereceiver. Portability is not an issue when the receiving apparatus is tobe mounted to, for example, a forklift. However, if receiving apparatusis to be incorporated into, for example, a mobile telephone, thenfurther miniaturisation of the receiver antenna is necessary.

The present invention describes an apparatus and method for utilisingantenna technology that is already deployed in portable hand-heldequipment in high-precision positioning applications.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome or ameliorate atleast one of the disadvantages of the prior art, or to provide a usefulalternative.

It is a further object of the present invention to create multiple beamssimultaneously.

It is a further object of the present invention to utilise antennatechnology that is already deployed in portable hand-held equipment inhigh-precision positioning applications.

It is a further object of the present invention to use a single RF frontend for simultaneously forming the multiple beams.

It is a further object of the present invention to form relativelynarrow beams using relatively large numbers of elements (generally morethan 32 elements), whilst minimizing electronic complexity.

It is a further object of the present invention to re-use standardpositioning receiver components/logic blocks to reduce powerconsumption, cost and complexity.

It is a further object of the present invention to provide a scalablesystem that is capable of making use of external receiver antennas toincrease the precision of the position solution.

It is a further object of the present invention to provide a method ofsimultaneously forming multiple beams in different directions usingrelatively large numbers of elements (generally more than 32 elements)for positioning systems, whist obviating the need for complicatedcircuitry and calibration.

According to one aspect of the invention there is provided a device forremotely forming a beam at antenna arrays, the device including:

-   -   an antenna array having a plurality of spatially distributed        elements;    -   a positioning-unit device coupled with said antenna array, said        positioning-unit device configured to switch said antenna        elements between first and second states in a predetermined        sequence wherein, in said first state, said elements are        configured to transmit a positioning signal; and    -   a receiver configured to receive said positioning signal from        said antenna array, said receiver having a processor for        generating a reference signal, mixing said positioning signal        with a modified reference signal to generate a mixed signal and        summing the mixed signal over a predetermined integration period        to generate an accumulated signal, wherein said reference signal        is modified prior to being mixed with said received signal such        that said accumulated signal is indicative of the direction and        magnitude of the beam of the antenna array.

Preferably, the receiver includes at least one receive channel having acorrelator, wherein the correlator is configured to selectivelymanipulate the phase and/or gain of the reference signal in substantialsynchronism with receipt of the positioning signal.

The positioning signal preferably includes a pseudorandom code having aunique chip sequence within a predefined chip period, the unique chipsequence being used to provide the substantial synchronisation betweenthe reference signal and the positioning signal. Preferably thepredetermined integration period is divided into a number ofsub-integration periods wherein each of the elements are switched to thefirst state for the duration of the sub-integration period.

The switching of each element to the first state is preferably alignedto a chip boundary within the unique chip sequence, wherein thesub-integration period is synchronised to begin at the same time as thechip boundary in the next chip period.

Preferably, each sub-integration period is configured to access arespective accumulator for storing the positioning signal, wherein eachrespective accumulator is mixed with the modified reference signal togenerate the mixed signal.

The duration of each sub-integration period within the predeterminedintegration period is preferably dynamically adjustable such that thepositioning signal transmitted from one or more elements are selectivelyexcluded from being mixed with the reference signal.

Preferably, the manipulation of the phase and/or gain is achieved byrespectively applying a phase and/or gain offset to the referencesignal, wherein the value of the phase and/or gain offset is calculatedin dependence upon the predetermined sequence.

The correlator preferably includes a carrier numerical controloscillator (NCO) and the reference signal is synthesised in the carrierNCO.

Preferably, the value of said phase and/or gain offset is calculated bythe processor in real time. Alternatively, the value of the phase and/orgain offset is calculated in advance and stored in a database that isavailable for retrieval by the processor.

Preferably, an element is active in said first state and inactive insaid second state. Preferably, elements switched to the second state areconfigured to be non-resonant such that the effects of mutual-couplingare ameliorated.

Preferably, the antenna elements are spatially distributed in a threedimensional configuration such that the device can form beams in one ormore dimensions.

Each receiver preferably includes multiple receive channels, whereineach receive channel is adaptable to form at least one beam.

According to another aspect of the invention there is provided a devicefor remotely forming a beam at an antenna arrays, the device including:

-   -   an antenna array having a plurality of spatially distributed        elements;    -   a positioning-unit device coupled with said antenna array, said        positioning-unit device configured to        -   a) switch said antenna elements between first and second            states in a predetermined sequence wherein, in said first            state, said elements are configured to transmit a modified            positioning signal; and        -   b) synthesise a positioning signal and modify said            positioning signal, in substantial synchronism with said            predetermined sequence, to generate a modified positioning            signal; and    -   a receiver configured to receive said modified positioning        signal from said antenna array, said receiver having a processor        for generating a reference signal, mixing said modified        positioning signal with said reference signal to generate a        mixed signal and summing the mixed signal over a predetermined        period to generate an accumulated signal such that said        accumulated signal is indicative of the direction and magnitude        of the beam of the antenna array.

According to another aspect of the invention there is provided a systemfor forming composite beams between antenna arrays, the systemincluding:

-   -   a transmit antenna array having a plurality of spatially        distributed elements, said transmit antenna array being coupled        to a positioning-unit device that is configured to switch said        antenna elements between first and second states in a        predetermined sequence wherein, in said first state, said        elements are configured to transmit a positioning signal;    -   a receive antenna array having a plurality of spatially        distributed elements, said receive antenna array being coupled        to a positioning receiver that is configured to switch said        antenna elements between first and second states in a        predetermined sequence wherein, in said first state, said        elements are configured to receive a positioning signal; and    -   said positioning receiver having a processor configured to:        -   receive said positioning signal from said transmit antenna            array, synthesize a reference signal:        -   modify said reference signal in substantial synchronism with            the switching of said elements of said transmit and receive            antenna arrays to the first state to generate a modified            reference signal;        -   mix said positioning signal with said modified reference            signal to generate a mixed signal; and        -   sum the mixed signal over a predetermined period to generate            an accumulated signal such that said accumulated signal is            indicative of the direction and magnitude of said beam of            said transmit and receive antenna arrays.

According to another aspect of the invention there is provided a methodfor forming a beam at antenna arrays, the method including the steps of:

-   -   a) switching, at a positioning-unit device, spatially        distributed elements of said antenna array from a second state        to a first state in a predetermined sequence, wherein, in said        first state, said elements are configured to transmit a        positioning signal;    -   b) receiving, at a receiver, a positioning signal;    -   c) generating, in a correlator of the receiver, a reference        signal for correlation with said positioning signal;    -   d) applying, in substantial synchronisation with receiving said        positioning signals, a predetermined offset to said reference        signal to create a modified reference signal;    -   e) mixing said positioning signal with said modified reference        signal to create a mixed signal; and    -   f) accumulating said mixed signal over an integration period to        create an accumulated signal, wherein said accumulated signal is        indicative of the direction and magnitude of said beam of said        antenna array.

According to another aspect of the invention there is provided a methodfor forming composite beams between antenna arrays, the method includingthe steps of:

-   -   a) switching, at a positioning-unit device, spatially        distributed elements of a transmit antenna array from a second        state to a first state in a predetermined sequence, wherein, in        said first state, said elements are configured to transmit a        positioning signal;

b) switching, at a positioning receiver, spatially distributed elementsof a receive antenna array from a second state to a first state in apredetermined sequence, wherein, in said first state, said elements areconfigured to receive a positioning signal;

-   -   c) receiving, at a positioning receiver, a positioning signal;    -   d) generating, in a correlator of said positioning receiver, a        reference signal for correlation with said positioning signal;    -   e) modifying said reference signal in substantial synchronism        with the switching of said elements of said transmit and receive        antenna arrays to the first state to generate a modified        reference signal;    -   f) mixing said positioning signal with said modified reference        signal to create a mixed signal; and    -   g) accumulating said mixed signal over an integration period to        create an accumulated signal, wherein said accumulated signal is        indicative of the direction and magnitude of said beam of said        transmit and receive antenna arrays.

According to another aspect of the invention there is provided a methodfor forming a beam at antenna arrays, the method including the steps of:

-   -   a) synthesising, in a positioning-unit device, a positioning        signal;    -   b) switching, at a positioning-unit device, spatially        distributed elements of said antenna array from a second state        to a first state in a predetermined sequence, wherein, in said        first state, said elements are configured to transmit a modified        positioning signal;    -   c) applying, in substantial synchronisation with the switching        of one of said elements to the first state, a predetermined        offset to said positioning signal to create said modified        positioning signal;    -   d) receiving, at a receiver, said modified positioning signal;    -   e) generating, in a correlator of the receiver, a reference        signal for correlation with said modified positioning signal;    -   f) mixing said modified positioning signal with said reference        signal to create a mixed signal; and    -   g) accumulating said mixed signal over an integration period to        create an accumulated signal, wherein said accumulated signal is        indicative of the direction and magnitude of said beam of said        antenna array.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic view of an antenna array coupled with apositioning-unit device according to one aspect of the invention;

FIG. 2 is a schematic view of the positioning receiver of FIG. 1 coupledto an omni-directional antenna showing some internal components of thereceiver according to one aspect of the invention;

FIG. 3 is a schematic view of a beam locally formed by the positioningreceiver interacting with a beam remotely formed by the antenna array ofFIG. 1;

FIG. 4 a is a timing diagram showing the relationship between B-slots,R-slots and the integration period according to one aspect of theinvention;

FIG. 4 b is a timing diagram showing in more detail the relationshipbetween B-slots, R-slots and how phase and/or gain offsets are appliedto the reference signal according to one aspect of the invention ;

FIG. 5 is a flow diagram of the steps involved for remotely formingbeams according to one aspect of the invention;

FIG. 6, is a schematic view of a modified correlator according to oneaspect of the invention; and

FIGS. 7 a and 7 b are schematic views of a two-antenna array accordingto one aspect of the invention.

PREFERRED EMBODIMENT OF THE INVENTION

System Overview

According to the invention, there is provided a device and method forforming a beam of a transmit antenna array in the direction of apositioning receiver. Since the beam of the transmit antenna array isformed remotely by the positioning receiver, the received gain of theincoming positioning signal is maximised while signals from otherdirections are attenuated, thereby mitigating any unwanted effects ofmultipath. Depending on the number of elements in the transmit antennaarray and their physical distribution, the width of the beam can be madefiner such that the positioning receiver only requires a simpleomni-directional antenna to achieve an accurate positioning solution. Infurther embodiments, the present invention can be combined with thedisclosure of WO 2011/000049 A1 to form composite beams for even greaterpositioning solution accuracy.

Referring to FIG. 1, a device 102 for forming remote beams between anomni-directional receive antenna and a transmit antenna array 104 havinga plurality of spatially distributed elements 106 is depicted. Apositioning-unit device 108 having an RF amplifier/modulator 126 iscoupled with the antenna array 104 and is configured to switch thetransmit antenna elements 106 between first and second states in apredetermined sequence, wherein, in the first state, the elements 106are configured to transmit positioning signals; and in the second statethe elements 106 are inactive.

A positioning receiver 114 is coupled with, in this case, anomni-directional antenna 112 and is configured to receive thepositioning signal from the transmit antenna array 104. The positioningreceiver 114 has a processor (not shown) for generating a referencesignal, mixing the positioning signal with a modified reference signalto generate a mixed signal and summing the mixed signal over apredetermined period to generate an accumulated signal, wherein thereference signal is modified prior to being mixed with said receivedsignal such that the accumulated signal is indicative of the directionand magnitude of the beam of the transmit antenna array 104.

In some embodiments, discrete components/logic blocks are used in acircuit utilizing mixers, oscillators and accumulators to produce therequisite accumulated signals before passing onto a positioning receiverfor subsequent processing. However, the preferred embodiment is toincorporate the beam forming method of the present invention into astandard positioning receiver, such as receiver 114, as much of therequired circuitry for forming beams according to the present inventionis already part of standard positioning receiver architecture in theform of the correlator, and only requires minor modification to allowthe formation of simultaneous beams.

FIG. 2 shows schematically the positioning receiver 114 used in atypical positioning network. The positioning receiver 114 makes use ofexisting components including at least one receive channel 202 having atleast one correlator 204 that is in communication with the processor206. Each correlator 204 incorporates a carrier numerically controlledoscillator (NCO) for generating a reference signal. The phase and/orgain of this reference signal is modified by the processor 206 insubstantial synchronism with the element switching sequence of thereceived positioning signal, thus creating a modified reference signal.The received positioning signal is subsequently mixed with this modifiedreference signal to create a mixed signal. This mixed signal is thenmixed with a code NCO reference signal, as per standard correlatorprocessing, and subsequently accumulated over a predeterminedintegration period to create an accumulated signal. The resultingaccumulated signal is therefore indicative of the direction andmagnitude of the beam 122 (shown in FIG. 1) formed within the correlator204 from the transmit antenna array 104. At the end of eachpredetermined integration period the tracking loops of the correlatoroperate as per normal correlator operation, unperturbed by the phaseand/or gain manipulations.

The beam of the antenna array can be formed remotely in one of two ways.According to one embodiment, the positioning-unit device 108 is equippedwith the logic to manipulate the phase and/or gain of the transmittedsignal directly. In this embodiment, the phase and/or gain offsets areapplied directly to the transmitted positioning signal in synchronismwith the switching of the elements 106 to the first state. For example,when the first element is switched to the first state, the applicablephase and/or gain offsets are calculated and used to manipulate thepositioning signal before the signal is transmitted via the firstelement. When the second element is switched to the first state, thenext set of phase and/or gain modifications is applied to thepositioning signal before the signal is transmitted by the secondelement, and so on for the rest of the elements. However, although thephase and gain modifications are applied by the positioning-unit device108, it is important to note that the beam 122 is not formed until thesignal is received by the positioning receiver 114 and is accumulatedfor an integration period equivalent to the time that elements of thetransmit array are switched according to the predetermined switchingsequence. Therefore, beam 122 is still, in effect, formed “remotely” bythe positioning receiver 114.

This method, however, is unsuitable for positioning systems because itis necessary for signal sources to be multiple access. That is, in apositioning network, there can be an unlimited number of positioningreceivers all configured to receive signals from a signal source. Byforming a transmit beam to one particular positioning receiver, otherpositioning receivers within the positioning network are thenindefinitely denied access to that signal source.

However, the preferred method for remotely forming beams is to switchthe transmit antenna elements in a predetermined switching sequence, butnot to change phase and/or gain at the transmit end. Changes to thephase and/or gain are made at the positioning receiver end bysynchronously manipulating the reference signal synthesised by thecarrier NCO in each correlator channel. In this way, all positioningreceivers within the network obtain the same switched, but non-modified,signals from the signal source. However, what is modified is simply thepositioning receiver's internal “copy” of the positioning signal. Thisallows a plurality of positioning receivers to form independent beamsfrom a single transmitter, thus creating a multiple access system. Asthis is the preferred method of remotely forming beams, this is themethod that will be discussed more fully herein.

Modification of the Reference Signal

After the reference signal is synthesised by the carrier NCO, it ismodified by selectively manipulating the phase and/or gain of thereference signal in substantial synchronism with receipt of thepositioning signal. Specifically, the manipulation of the phase and/orgain is achieved by applying a phase and/or gain offset to the referencesignal, wherein the value of the phase and/or gain offset is calculatedin dependence upon the predetermined sequence that the elements 106 ofthe transmit antenna array 104 are switched between the first and secondstates.

The transmit antenna array 104 is operatively associated with thecorrelator 204 through synchronous insertion of the respective phaseand/or gain offset within the correlator circuit. The operation of thecorrelator and the insertion of the phase and gain offsets are describedin further detail below, with reference to FIG. 6.

Referring again to the embodiment of FIG. 2, the value of the phaseand/or gain offset is determined by retrieving a predetermined valuestored in a database 208 that is accessible by the processor within thepositioning receiver. An offset table, such as the table shown in theillustrative example below, is stored in the database 208 andselectively accessible by the processor 206. Although a stored databaseof predetermined offset values for a known distribution of antennaelements is illustrated, this is not necessarily the preferred method.It will be understood by those skilled in the art that in alternativeembodiments, the phase and/or gain offsets are calculated in real timeby the processor 206, utilizing an a-priori model of the antenna array.That is, using the known distribution of antenna element positions tocalculate the requisite phase and/or gain to produce the required beams.

Antenna Elements

In the embodiments shown in the various figures, patch elements aredepicted in a 3×3 array. However, it will be understood by those skilledin the art that in other embodiments, monopoles, dipoles or othersuitable antenna elements are utilised. It will be further understoodthat the disclosure herein applies equally to antenna elements deployedin antenna arrays having multiple dimensions. In fact, in many practicalapplications, antenna elements are spatially distributed in athree-dimensional shape.

Throughout this specification and in the claims, the “first” staterefers to when an element is active and the “second” state refers towhen an element is inactive. The actual implementation of the inactivestate varies depending on the type of element used, with the focusplaced on making elements non-resonant to mitigate the effects ofparasitics or mutual-coupling. For example, a ¼λ monopole element isswitched to open in the second state while a patch element is switchedto ground in the second state. In some embodiments, the switches alsoprovide a connection to a resistance, such as 50 Ω in the second state.It will be appreciated by those skilled in the art that switching toother conditions, such as reactive loads, are also possible in thesecond state.

Beam Forming Slots

In the preferred embodiment, only one element 106 is in the first stateat a time during the predetermined integration period of the positioningreceiver, while all other elements are in the second state. That is, foreach beam formed at the completion of the predetermined integrationperiod of the positioning receiver, each element 106 has transmitted atleast once within the integration period. Each element 106 is switchedto the first state for the duration of a sub-integration period, whichis less than the predetermined integration period. In one embodiment,these sub-integration periods are known as “remote beam forming slots”(R-slots).

The relationship between R-slots and the integration period is bestshown in FIG. 4 a, which shows R-slots 402 that are each 1 μs in lengthand the integration period is Nμs long. In essence, the length of theintegration period is simply divided into a number of R-slots equal tothe number of elements on the antenna arrays. Although preferred, itshould be noted that there is no requirement that the R-slots be ofequal length, or that only one element is switched to the first state atone time. An R-slot is therefore simply a period of time, during whichthe positioning receiver 114 is configured to receive a positioningsignal transmitted from any element in the transmit antenna array 104that is switched to the first state. The signal segment within theR-slot is manipulated by the positioning receiver by modifying it with apredetermined phase and/or gain offset, before all the R-slots areaccumulated at the end of the integration period to form a beam.

In one embodiment, the minimum number of required R-slots corresponds tothe number of elements 106 that are spatially distributed on thetransmit antenna array 104. For example, in an implementation where theantenna array only includes two elements, the minimum number of requiredR-slots is two. When an element 106 is switched to the first state, thereceiver is configured to receive the transmitted positioning signal forthe entire duration of the allocated R-slot.

In a further embodiment, ten elements are spatially distributed in atransmit antenna array and ten R-slots are provided, one for eachelement. Using an integration period of 1000 μs, which is a typicalintegration period of a standard GPS receiver, elements are switched tothe first state for a period of 100 μs each, in a predetermined sequence(such as sequentially or pseudo randomly). The positioning-unit device108 switches the first element to the first state and beginstransmitting the positioning signal. Once the positioning receiver 114receives the transmitted signal, and synchronisation to the transmittedR-slots has occurred, the processor 206 determines the phase and/or gainoffset that needs to be applied to the reference signal, whichcorresponds to the first element's position within the transmit antennaarray 104 and the direction of the beam required by the positioningreceiver 114. The offsets are then applied to the reference signal forthe entire duration of the first allocated R-slot. In the subsequent 100μs R-slot, the positioning-unit device 108 switches the second elementto the first state while the first element and all the other elementsare switched to their second states. Again, the processor 206 of thepositioning receiver 114 determines the phase and/or gain offsetcorresponding to the second element's position within the array and thedirection of the beam required by the positioning receiver, and appliesthat phase and/or gain offset for the entire duration of the secondR-slot. In this example, which uses a sequential switching scheme, thepositioning-unit device then switches the third element to the firststate while the other elements are switched to their second states forthe third R-slot, and so on for the subsequent elements and R-slotswithin that integration period. At the completion of the 1000 μsintegration period, all ten 100 μs R-slots will be accumulated with therequisite phase and/or gain offsets to produce the desired beam requiredby the positioning receiver.

It should be noted that the positioning-unit device 108 is physicallyseparate from the positioning receiver 114, and therefore the individualelements 106 in the transmit antenna array 104 cannot directly accessthe receiver 114. However, the positioning receiver 114 knows, a priori,the sequence in which the elements 106 in the transmit antenna array 104will be switched to the first state, the distribution of elements withinthe transmit array, and the orientation of the transmit array. In thepreferred embodiment transmit array information, incorporating theantenna element switching sequence and the geographical position of eachindividual antenna element, is broadcast from each positioning-unitdevice to all positioning receivers in-view. In substantial synchronismwith the positioning receiver 114 receiving the transmitted positioningsignal R slots, the phase and/or gain of the reference signal ismanipulated as appropriate in order to form the beam in the desireddirection. Also, in order to obtain the full benefit of the allocatedR-slot, it follows that the phase and/or gain manipulation must beapplied to the reference signal throughout the entirety of the allocatedR-slot.

As the positioning receiver 114 controls the direction of the beamformed by the transmit antenna array 104, this method of beam forming istermed “remote beam forming”, and the slots used to accumulate thetransmitted positioning signals are known as R-slots.

In addition, and as discussed in WO 2011/000049 A1, it is also possiblefor the positioning receiver 114 to be configured to form “local” beamsusing a receive antenna array that is directly connected to thepositioning receiver 114. This works in a similar fashion to remote beamforming, but with a significant difference. In remote beam forming, thepositioning receiver 114 synchronises R-slot switching of eachcorrelator channel independently, the timing of this synchronisationbeing dependent on the distance of the positioning receiver from eachtransmitter. In local beam forming, the positioning receiver directlycontrols the switching of the elements in the receive antenna array. Asan element is switched to the first state, the positioning receiversimultaneously manipulates the phase and/or gain of each referencesignal across all correlator channels and, once mixed and accumulated, aunique receive antenna beam is formed in each correlator. Again, theintegration period for local beam forming is divided into slots called“beam forming slots” or B-slots.

It follows therefore, that both local and remote beam formingmethodologies may be combined to form composite beams to provide anaccurate position solution. This is best shown in the embodiment of FIG.3, in which the positioning-unit device 108 is coupled with a transmitantenna array 104 as previously discussed. The positioning receiver 114is also coupled to a receive antenna array 302 which, in this casecomprises patch elements 304 configured in a 3×3 matrix similar to thetransmit antenna array 104. Transmit beam 122 and receive beam 308 areformed such that they track each other, as shown, providing, in essence,a point-to-point communication link between the positioning receiver 114and the positioning-unit device 108.

In this embodiment, both remote and local beams are formed in thecorrelator of the positioning receiver 114. As best shown in FIG. 4 a,the integration period is divided into both B-slots 404 and R-slots 402,where some R-slots 402 may overlap B-slots 404. Therefore, in someinstances, the phase and/or gain of the reference signal may be modifiedboth in connection with the current active B-slot 404 and in connectionwith the current active R-slot 402 to give the required composite beam.This is because the B-slot manipulation is triggered directly by thepositioning receiver 114 when an element in the local receive antennaarray is switched to the first state while the R-slot manipulation istriggered independently across each channel according to the receivedR-slot timing, and in conjunction with the predetermined switchingsequence of the transmit antenna array 104. This timing is affected byindividual propagation delays between each transmitter and thepositioning receiver.

The process of forming composite beams is best shown in the embodimentof FIG. 4 b, which is a timing diagram for a hypothetical positioningsystem using 64 element antenna arrays on both the transmit side and onthe receive side. First, note that R-slots 406 are unique to a singlechannel, while B-slots 408 are common across all channels. This isbecause, as discussed above, R-slots are triggered independently acrosseach channel whereas all B-slots are triggered at the same time by thepositioning receiver as elements in the receive antenna array areswitched to the first state.

Referring to the transmit antenna array, as the chip sequence boundary410 ticks over, at point 412, element 1 of the transmit antenna isswitched to the first state, and begins transmitting the positioningsignal segment to form the next beam (denoted “beam B” in FIG. 4 b). Atthis point, the first R-slot begins, and the R-slot sequence for thischannel is synchronised from point 412 onwards. As shown in FIG. 4 b,the phase and/or gain offset that is applied to the reference signal forthe first R-slot for beam B is denoted {B}₁.

Concurrently and, asynchronously, to the R-slot sequence, the receiveantenna array is also switching B-slots. Just prior to point 412, thereceive antenna array is forming a beam (denoted “beam X”) and isreceiving a signal from element 63 of the receive antenna array; theoffset being applied to the reference signal in respect to the receivedsignal is denoted {X}₆₃. At point 412, the positioning receiver updatesthe remote transmit beam look-angle from “beam A” to “beam B”, and thelocal receive beam look-angle from “beam X” to “beam Y”. This causes thepositioning receiver to stop applying the remote transmit phase and/orgain offset denoted by {A}₆₄ to the reference signal and start applyingthe phase and/or gain offset denoted {B}₁ to the reference signal.Concurrently, the positioning receiver stops applying the local receivephase and/or gain offset denoted by {X}₆₃ to the reference signal andstarts applying the phase and/or gain offset denoted {Y}₆₃ for the restof the 63^(rd) B-slot to the reference signal. The positioning receiverthen continues switching the elements of the receive antenna arrayaccording to the predetermined sequence, but is now forming local beam Ythrough the application of the phase and/or gain offsets denoted {Y}_(n)to the reference signal, and forming remote beam B through theapplication of the phase and/or gain offsets denoted {B}_(n) to thereference signal.

In the preferred embodiment, the R-slot and B-slot phase and/or gainoffset values are combined (preferably, the phases are summed and thegains are multiplied), as shown in the RX/TX Combined Phase/Gain Offset414. The combined offset value is then applied to the reference signalto form composite beams between the transmit antenna array and thereceive antenna array as best shown in FIG. 3.

Synchronisation

For local beam forming, each element of the receive antenna array isconnected to a respective switch, which in turn feeds into a single RFfrontend to be downconverted and sent to the correlator. Generally,transmission lines that interconnect the elements and the switches areof equal length, to ensure received signals are phase coherent throughthe antenna array feed system. However, in some embodiments, differencesin the lengths of the transmission line are taken into account andcorrected at the time of applying the phase and/or gain offsets.

The interconnection between the receive antenna array and thepositioning receiver, as well as the RF frontend, the electronicsinvolved in the correlator and the actual switches themselves, willinevitably cause delays. In one implementation, this delay is measuredto be around 950 ns, but of course, those skilled in the art willappreciate that the length of the delay will vary depending on theselected hardware. Therefore, operation of the phase and/or gainmanipulation in the correlator cannot occur simultaneously with theswitching of the element to the first state, as this delay must beaccounted for. That is, the manipulation of the phase and/or gain in thecorrelator must be delayed by up to 950 ns in this embodiment.

In a physical implementation, the receive antenna array contains 64elements with an integration period of 100 μs. Therefore, the period ofa B-slot is in the region of just 1 μs or 2 μs and, as such, a delay ofnearly 1 μs is significant and must be accounted for.

Therefore, for local beam forming, the first B-slot of the integrationperiod for each correlator 204 of the positioning receiver 114 areupdated simultaneously and triggered to start after taking this 950 nsdelay into account.

However, for remote beam forming, each correlator starts asynchronouslyas each correlator is individually updated and triggered based on whenthe positioning signal is received. That is, the synchronisation processrequired for remote beam forming is markedly different from thesynchronisation required for local beam forming.

The positioning-unit device 108 switches an element to the first statewhich then begins transmitting the positioning signal. The positioningreceiver must be synchronised so that it manipulates the phase and/orgain of the reference signal as the element 106 is switched to the firststate, taking into account propagation and receiver delays before thesignal is received in the correlator. In addition, there is atransmission delay that occurs between when the positioning signal isgenerated and when it is transmitted through the antenna, which isprimarily introduced by the RF modulator/amplifier 126. In practice,this transmission delay is similar to that incurred in the receiver andis usually around 950 ns.

In the preferred embodiment, the chip sequence of the pseudorandom code(PRN) generator of the positioning-unit device is used as a quasi-timerto trigger the R-slot sequence. This method has the additional benefitof negating the effects of the propagation and receiver delays, but thetransmitter delays must still be accounted for.

For this embodiment, it is assumed that the positioning receiver 114knows, a priori, the switching sequence of the transmit antenna array104, the type of antenna array 104 that is coupled to positioning-unitdevice 108, as well as the antenna array 104 position and orientation.This information therefore provides the precise geographicalco-ordinates of each individual antenna element to the positioningreceiver 114.

In a positioning-unit device, the PRN code is a random but finite binarysequence, which is unique for every positioning-unit device and, in thisembodiment, is 1023 chips long. That is, the PRN code repeats every 1023chips for a given positioning-unit device 108. Since the positioningreceiver knows that the received positioning signal will be 1023 chipslong, it can define R-slot durations with reference to a chip period.

For example, if the transmit antenna array consists of 50 elements, andthe sequence length of the PRN code is 1023 chips, then an R-slot, inthis embodiment, is defined as a period of time within the integrationperiod equivalent to 20 chips (rounded down to the nearest integer).Furthermore, the elements 106 are configured to switch states, in apredetermined sequence, in synchronism with a boundary chip of anR-Slot.

For example, assume that elements 106 are set to switch in a sequentialswitching sequence starting from element 1 and that chip 1 of the PRNcode is set to be the beginning of the first R-slot. When chip 1 of thenext integration period ticks over, the positioning-unit device 108switches element 1 to the first state and begins transmission of thepositioning signal. Similarly, when the 21^(st) chip ticks over thesecond R-slot begins and the positioning-unit device 108 switches theelement 2 to the first state while switching element 1 and the otherelements to the second state. At the 41^(st) chip the third R-slotbegins and element 3 switches to the first state, and so on for all therest of the elements.

As explained in more detail below, once the positioning receiver 114receives the positioning signal, it correlates the received PRN codesequence against an internally generated PRN code sequence, thusbringing the internally generated code sequence into alignment with thereceived PRN sequence. Therefore, the positioning receiver 114 is alsoconfigured to “count” the chips in the code sequence to determine theboundary chip that triggers the next R-slot.

Knowing the current R-slot, and the associated element in the transmitantenna array 104 that is switched to the first state, the positioningreceiver 114 can then calculate the appropriate phase and/or gain offsetvalue to apply to the reference signal so as to obtain the desireddirection to in which point the beam 122 at the end of the integrationperiod.

Beam Forming Methodology

The steps followed to form beams using the device disclosed herein aregraphically represented in the flow diagram of FIG. 5. A description ofthe steps taken is provided below.

-   -   a) At step 502, one of the spatially distributed elements in the        transmit antenna array is selected.    -   b) At step 504, the element selected at step 502 is switched to        the first state.    -   c) At step 506, the element switched to the first state at step        504 begins transmission of the positioning signal in a        predetermined R-slot.    -   d) At step 508, an internal reference signal, based on the known        PRN code sequence to be received, is generated in the correlator        for mixing with the incoming positioning signal.    -   e) At step 510, a predetermined offset is applied to the        reference signal, in substantial synchronisation with the        currently received predetermined R-slot positioning signal, to        create a modified reference signal.    -   f) At step 512, the modified reference signal is mixed with the        received positioning signal to create a mixed signal.    -   g) At step 514, the mixed signal is accumulated in the        accumulators to create an accumulated signal.    -   h) At step 516, the selected element is switched to the second        state, the next element is switched to the first state in the        next R-slot and the process starts again from step 502.    -   i) At step 518, after accumulating all the R-slots together at        the end of the integration period, a beam is formed in the        accumulators based on the value of all the R-slot signals.    -   j) At step 520, the carrier and code lock loops are updated        using the accumulated R-slot signals.

Correlator Operation

A GPS position receiver typically uses a logic block called a correlatorto correlate an incoming positioning signal with internally generatedreference signals. Referring to FIG. 6, in the correlator 204, anincoming positioning signal is mixed with two internally generatedreference signals. The first reference signal is a carrier referencesignal that is generated by the carrier NCO 608. Mixing the carrierreference signal with the incoming positioning signal generates an errorsignal representing a phase and frequency difference between the carrierreference signal and the incoming signal. The second reference signal isa code reference signal that, in this embodiment, is generated by thecode NCO 616. Once the incoming positioning signal has been mixed withthe carrier reference signal, the incoming positioning signal is mixedwith the code reference signal, which generates an error signalrepresenting the time delay between the code reference signal and theincoming positioning signal.

For simplicity, FIG. 6 only shows a single receive channel of apositioning receiver. However, those skilled in the art will appreciatethat modern receivers typically include more than a single receivechannel, with each channel typically including more than one correlator.

In FIG. 6, the incoming positioning signal is received at the input 602and stripped of the carrier component by mixing, in mixers 604 and 606,the incoming signal with a reference carrier signal to produce in-phase(I) and quadra-phase (Q) sampled data. The reference carrier signal issynthesised in the carrier NCO 608 and the discrete sine and cosinemapping functions 610 and 612 respectively. This stripping processproduces I and Q signals as shown. In operation, the carrier NCO iscontrolled by the carrier lock loop 614. The objective of the carrierlock loop is to keep the phase error between the reference signalgenerated by the Carrier NCO and incoming positional signal at, or asclose as possible to, zero. When the phase error is zero, the signalsare said to be “phase-locked” and the I signals are at a maximum whilethe Q signals are nearly zero. This operation is also called “phase lockloop” (PLL) operation.

The I and Q signals are then correlated with a reference code signalthat, in this embodiment, is synthesised in the code NCO 616. For thesake of simplicity, only one reference code signal is synthesised inthis embodiment. However, those skilled in the art will recognise thatin most positioning receivers, more than one code reference signal issynthesised. For example, in one application, three code referencesignals—early, prompt and late signals—are synthesised and separatelycorrelated with the I and Q signals respectively.

The correlator 204 mixes an internally synthesised code reference signalwith the incoming I and Q signals in the mixers 614 and 620. Inoperation, the code NCO 616 is controlled by the code lock loop 626. Theobjective of the code lock loop is to keep the time error between theinternally generated code reference signal and incoming code positioningsignal at, or as close as possible to, zero. When the time error iszero, the signals are said to be “code-locked”. This operation is alsocalled “delay lock loop” (DLL) operation.

That is, the operation of the code lock loop 626 is similar to thecarrier lock loop 614. When the reference signal code phase iscompletely aligned with the incoming positioning signal code phase,maximum correlation is attained.

The resultant mixed signals are then integrated in the accumulators 622and 624 over an integration period, providing I_(p) and Q_(p) signals,which are subsequently accessed by the processor 206 for tracking loopoperation.

The integration period refers to the length of time over which thereceived signal is accumulated, and is traditionally determined based ona satellite's pseudorandom code noise length or multiples thereof. InGPS, this code period is 1 ms, and thus the integration period in thereceiver is also often set to 1 ms or more.

Phase and/or Gain Offsets

In a preferred embodiment, phase and/or gain offsets for manipulatingthe phase and/or gain of the transmitted positioning signal is insertedat point 628, after the carrier reference signal is synthesised by thecarrier NCO 608 and before the synthesised carrier reference signal ismixed with the carrier component of the incoming positioning signal,completing the carrier lock loop 614. In this preferred embodiment thephase offsets are summed with the synthesized carrier reference signal,and the gain offsets are multiplied with the synthesized carrierreference signal. Manipulation of the incoming positioning signal isachieved by modifying the synthesised carrier reference signal withinthe integration period of the correlator, therefore not interfering withthe normal operation of the carrier NCO 608 or the carrier lock loop614. The modified reference signal is then mixed with the incomingpositioning signal in the usual manner, and the mixed signal isintegrated in the accumulator over the integration period to create anaccumulated signal.

As known by those skilled in the art, the integration of a waveform issimply the summation of samples of that waveform over a given period oftime, in this case, the integration period. Therefore, the integrationof the resultant mixed signal (resulting from mixing the incoming signaland the reference signal) is simply the summation of samples of thatsignal over a period of time—which in one of the embodiments describedabove is the integration period of 1 ms.

In one embodiment, the positioning signal is received at a rate of 75MHz and the samples are then mixed with a modified reference signal,which is also synthesised at 75 MHz. Consequently, for a hypotheticalsystem in which the integration period is 1 ms comprised of 10 R-slots,each R-slot is of 100 μs in duration and therefore contains 7,500samples of the incoming positioning signal. Each one of these 7,500samples is sequentially mixed with a modified reference signal to form amixed signal. The modified reference signal is based on a phase and/orgain offset applied to a reference signal, the reference signal beinggenerated by the carrier NCO of the correlator.

Specifically, for each block of 7,500 samples of the incomingpositioning signal, which are synchronized with antenna elements beingin the first state, the reference signal is modified by applying a phaseand/or gain offset to the output of the carrier NCO. This modifiedoutput is then multiplied (mixed) with the incoming positioning signalsamples. These mixed signals are then passed through the code NCOmixers, as per normal correlator operation, and then summed in theaccumulators to form an accumulated signal. Therefore over the entireintegration period of 1 ms, 75,000 samples, incorporating ten R-slotblocks of 7,500 modified samples each, are summed and stored in theaccumulators. In other words, these ten R-slots contain 7,500 modifiedsamples each of which are summed together in the accumulation process,and the 75,000 accumulated samples at the end of the integration periodare therefore representative of the desired beam 122. As shown in FIG.6, the desired beam is pointed in the direction of omni-directionalantenna 112 which is coupled with the positioning receiver 114.

Once the phase and/or gain manipulations are correctly applied to thereference signals and mixed with the signals received from therespective elements, the resultant mixed signal is then combined in theaccumulator (the summing process) to create an accumulated signal,forming the desired beam in the correlator. This accumulated signal isthen processed in the correlator as per normal PLL operation asdiscussed above. The carrier reference signal synthesised by the carrierNCO 608 does not change during the integration period, but is onlyupdated by the carrier lock loop 614 at the end of each integrationperiod. Therefore, phase and/or gain modifications to the referencesignal within the integration period are applied against a commoncarrier NCO 608 value, and cannot be detected by the PLL or the DLL. ThePLL and DLL operate as per normal, unaware of the manipulations takingplace.

Through the embodiments described, the use of a conventional correlatoris adaptable to control the direction and the width of a unique beam percorrelator channel, thereby allowing multiple simultaneous beams to beformed. The number of beams able to be formed is equal to the number ofcorrelator channels available. This is because the correlator alreadycontains logic for mixing and integrating signals—these are simplyadapted for a use other than correlating.

Although the embodiments described above apply offsets to both the gainand the phase at point 628 in the correlator circuit, in otherembodiments, additional multipliers for applying gain offsets areprovided in other parts of the circuit. For example, multipliers can beadded in the In-phase and Quadra-phase paths between the carrier NCOmixers and the code NCO mixers to provide gain manipulation. Similarly,phase offsets can also be applied at other parts in the correlatorcircuit. For example, phase offsets can be added to the output of thecode NCO.

In the preferred embodiment, the phase and/or gain offsets for formingthe transmit beam 122 (of FIG. 3) in any given direction are calculatedin hardware as and when required. The processor 206 of the positioningreceiver determines the direction of the required beam, and calculatesthe correct phase and/or gain offsets for each element in each R-slotover the integration period to form the beam in the desired direction,and inserts the necessary offsets at point 628 such that the beam isformed in the direction of the positioning receiver 114. As also noted,obtaining and inserting the phase and/or gain offsets for the transmitbeam must be substantially synchronous with the receipt of the R-slotsso that the phase and/or gain is correctly manipulated over theintegration period.

Similarly, the phase and/or gain offsets for forming the local receivebeam 308 (of FIG. 3) in any given direction are also calculated. Theprocessor 206 determines the direction of the transmit beam 122,calculates the correct phase and/or gain offsets for each element of thereceive antenna array 302 (of FIG. 3) in each B-slot over theintegration period to form the receive beam 308 in the directioncorresponding to the transmit beam 122, and inserts the necessaryoffsets at point 628 such that the beams are formed in the appropriatedirection. Obtaining and inserting the phase and/or gain offsets for thereceive beam 308 must be substantially synchronous with the switching ofthe respective elements 304 of the local antenna array into the firststate so that the phase and/or gain is correctly manipulated over theintegration period.

In other embodiments, the phase and/or gain offsets for forming both theremote transmit beam 122 and the local receive beam 308 in any givendirection are predetermined, and stored in the database 208 (of FIG. 2)and is accessible by the processor 206. The format of the offset datacan take many forms, such as in an offset table. The processor 206determines the direction of the required beams, accesses the database208 to obtain the correct phase and/or gain offsets for each elementover the integration period to form the beams in the desired directions,and inserts the necessary offsets at point 628 such that the beams areformed in the appropriate direction.

The number of elements that the antenna array contains is one criterionfor forming narrow beams. Other, equally important criteria include thespeed of the calculation of the phase and/or gain offsets and thephysical spacing of the elements. For example, in embodiments having 60elements, each direction in which a beam is to be formed must have 60gain offsets and 60 phase offsets, which in this embodiment arecalculated in real time in hardware.

The physical separation of the elements is also important so as tocreate a phase difference between the elements. Effectively, thephysical separation of the elements allows a positioning signal to betransmitted with inherently different phases. One half wavelengthseparation between elements provides maximum phasing with minimumgrating lobes. Manipulation of those phases, for example by mixing witha modified reference signal as noted above, allows for a beam to beformed in a desired direction.

In a particularly preferred embodiment, the elements 106 are spatiallydistributed in a configuration that is more than two dimensions suchthat the device can form beams in more than two dimensions. To a largeextent, the directions in which a beam can possibly be formed aredependent on the elements used. For example, a planar array consistingof patch elements will be able to form beams hemispherically and aplanar array consisting of monopoles will be able to form beams in aplane.

Angle of Arrival vs Angle of Transmission

Traditionally, angle of arrival solutions work by estimating the angleof a signal arriving at a base station with respect to a referencedirection, such as geographic north. A plurality of receive elements arespatially distributed at the base station and phase comparisonsperformed to determine an angle of arrival of a transmitted signal froma user terminal. If a number of such base stations are available theposition of the user terminal can be calculated by the network of basestations, using intersection of angles.

However, this technique only allows the network to perform the positioncalculation, not the user terminal. The user terminal is unaware of itsown position.

However the present invention overcomes this limitation, and makes itpossible for the position receiver to calculate its own position usingwhat, for the purposes of this discussion, is termed “angle oftransmission”. Conceptually, the angle at which a positioning signal istransmitted from a positioning-unit device, if known, can be used in asimilar manner to the angle of arrival to calculate the position of thepositioning receiver. However, since a positioning signal is typicallybroadcast so that multiple positioning receivers can access the signaland calculate their respective positions, it is not possible tocalculate an “angle of transmission”.

In the present invention however, it is possible for the positioningreceiver to form a beam from the transmission source directed at thepositioning receiver itself. Therefore, with the orientation of thetransmission array known a-priori, an angle of transmission can bedetermined from each transmission source. The position receiversubsequently uses a plurality of geographically distributed signalsources to calculate a position using intersection of angles. Moreover,in one embodiment, the positioning receiver is only equipped with asimple omni-directional antenna. In such an embodiment, it is impossiblefor the positioning receiver to calculate its position using standardangle methods such as angle of arrival. It must instead rely on theangle of the beam from the transmission source.

An Illustrative Embodiment

For illustrative purposes, the invention will now be described using thesimplest antenna array—an array having only two elements as shown inFIGS. 7 a and 7 b. However, those skilled in the art would be able toadapt the teachings herein to antenna arrays having many more elementsspatially distributed in multi-dimensional shapes without additionalinventive faculty.

In this illustrative embodiment, elements 702 and 704 are quarterwavelength mono poles. The two elements are placed a half wavelengthspatially apart from each other at known geographical locations andphase coherent signals are transmitted by each element. When the signalstransmitted by the two elements are summed together, the respectiveomni-directional gain patterns of the elements combine such that, from atwo dimensional topographical view of the elements, a figure-8 beampattern is formed, as shown in FIG. 7 a. In this configuration, anoutgoing positioning signal from the broadside direction of the elements702 and 704 is in-phase, and hence summed constructively, while signalsfrom the end-fire direction of the elements are out of phase, and hencecancelled.

Phase Manipulation

In the present invention, it is possible to rotate the figure-8 by 90°so that maximum gain is pointed in the end-fire direction, as shown inFIG. 7 b. This is achieved by manipulating the phase and/or gain ofelement 702 and element 704 within an integration period of a positionreceiver. Element 702 and element 704 are each connected to a switch, sothat either element can be switched between first and second states bythe positioning-unit device and the integration period over which thesummation of the signal occurs is split into two R-slots.

Since the phase separation between elements 702 and 704 is known, thephase of one of the elements can be manipulated so that transmittedwaves from the end-fire direction are summed constructively instead ofdestructively. In this case, because the elements are half wavelengthapart, the phase manipulation required at element 704 is 180°. The phasemanipulations required for each direction are similarly calculated toconstruct an offset table. For the sake of simplicity, the gain offsetis set at 1 and the direction that the beam can be steered is limited toeither the broadside direction or the end-fire direction. An exampleoffset table incorporating these limitations is provided below.

Direction Broadside End-fire Element 702 704 702 704 Phase 0° 0° 0° 180°Gain 1 1 1 1

To form a beam in the end-fire direction, elements 702 and 704 areswitched to the first state in a predetermined sequence. First, at thetransmission end, element 702 is switched to the first state and startstransmitting a positioning signal. When the signal from element 702 isreceived at the receiver end, the first R-slot begins and the phaseoffset is kept at 0° while being accumulated in the accumulator—nomanipulations are necessary because this element is already at 0°. Next,element 704 has a received phase of 180° relative to element 702 in theend-fire direction, and the phase of the positioning signal is desiredto sum constructively with element 704 in this direction. Therefore,when the positioning signal is received by the positioning receiver inthe second R-slot, a phase offset of 180° must be added to the signalreceived from element 704, so that the transmitted signal from element704 becomes phase coherent with element 702. The two R-slots are summedtogether in the accumulation process and the accumulated value at theend of the integration period is therefore representative of theend-fire beam.

It will be understood by those skilled in the art that in the presentinvention, the figure-8 beam can be formed in any direction, dependingon the complexity of offset table.

For both elements in this simple example, a gain offset of 1 (unitygain) is multiplied with the incoming positioning signal and thereforedoes not modify the beam formed. Appropriate gain offsets allowmodification to the shape of the beam, thus allowing mitigation ofgrating lobes, which is well known in the art of phased arrays and not asubject of the present invention.

As noted above, the phase manipulation must be applied substantiallysynchronously to the receipt of the positioning signal from the elementbeing switched to the first state; otherwise the gain pattern of thebeam will not be formed correctly.

According to embodiments of the present invention, a positioning signalcommences transmission from the first element. After acquisition of thispositioning signal by the positioning receiver, a carrier NCO within thepositioning receiver correlator synthesises a reference signal that issubstantially similar to the positioning signal.

The positioning receiver determines that it is in the end fire directionrelative to the positioning-unit device, and therefore a decision ismade to form a beam in that direction. The receiver processor calculatesand determines that no offset is required for the first R-slot duringthe integration period, which corresponds to element 702. Similarly, theprocessor determines that a 180°, or ½λ, offset is required during thesecond R-slot, which corresponds to element 704. After applying eachoffset to the carrier NCO to create a modified reference signal, theincoming positioning signal and the modified reference signal are mixedin a mixer and accumulated in the accumulator, as per the normaloperation of a correlator.

The received positioning signal is stripped into its in-phase andquadra-phase components, by mixing the received positioning signal witha carrier reference signal that is synthesised by the carrier NCO 608and the discrete sine and cosine mapping functions 610 and 612, as shownin FIG. 6. Before the modified reference signal is mixed with thereceived positioning signal, however, the processor determines that thepositioning receiver is in the endfire direction of the positioning-unitdevice. For the first R-slot, which corresponds to the time that thepositioning receiver receives the positioning signal from element 702,the processor calculates that an offset is not required and so nomodifications to the reference signal are necessary. The accumulation istherefore allowed to proceed as per normal correlator operation. Thatis, the unmodified reference signal is mixed with the receivedpositioning signal in mixers 604 and 606 to create a mixed signal, thenmixed with the code reference signal, and subsequently accumulated inthe accumulators 622 and 624.

For the second R-slot, the processor calculates that a phase offset of180° is required. The offset is applied to the current carrier referencesignal phase value to create a modified reference signal as the secondR-slot begins and the positioning signal from element 704 is received.The phase offset is applied continually to the carrier NCO valuethroughout the duration of the R-slot. The modified reference signal ismixed with the received positioning signal to create a mixed signal,then mixed with the code reference signal, and subsequently accumulatedwith the value of the first R-slot in the accumulators 622 and 624 tocreate an accumulated signal. The two R-slots are therefore summedtogether in the accumulation process and the accumulated value at theend of the integration period is therefore representative of theend-fire beam.

Note that the carrier reference signal synthesised by the carrier NCO608 does not change during the integration period, but is only updatedby the carrier lock loop 614 at the end of the integration period.

In embodiments discussed herein, the accumulated signal is created inthe accumulator over the entire duration of the integration period.However, in other embodiments, each R-slot is accumulated in its ownindividual accumulator, the minimum number of accumulators correspondingto the minimum number of R-slots required. In these embodiments, theaccumulated signal is obtained from combining the signals in theindividual accumulators.

In the embodiments discussed, only one element can be in the first stateat any instant within the integration period. Therefore, when element704 is switched to the first state, element 702 is simultaneouslyswitched to the second state.

After traversing the code lock loop 626, the mixed signal is integratedin the accumulators 622 and 624, creating an accumulated signal. Sincethe manipulation to the signals occurs serially, the integration of themixed signal is, in effect, the summation of an infinite number ofmodified signals over the integration period. Therefore, the accumulatedsignal is representative of a new beam formed in the desired direction.

Advantages, Applications and Usage

As described above, the antenna array and switching circuit are coupledto the positioning-unit device, while a physically separate positioningreceiver performs the required PVT solution to determine the position ofthe receiver. Since the sequence that the elements of the transmitantenna array are switched to the first state is predetermined, thetransmit antenna array type and orientation are known, and thepositioning receiver position can be determined, the beams formed ineach correlator channel can be directed towards the positioning receiverto maximise the gain of the incoming signal received by the positioningreceiver while attenuating signals from other directions, thereforemitigating the effects of multipath.

Current positioning technologies, such as GPS, work well in environmentsthat have direct access to three or four positioning signals. Howeverexisting systems are not as useful in closed environments due to theprevalence of multipath.

One solution to restrict multipath is through the formation of beamsusing an antenna array. As discussed in PCT/AU2010/000839, an antennaarray is coupled with the positioning receiver to form a beam to receivea positioning signal which is transmitted from the positioning-unitdevice via a simple omni-directional antenna.

This specification describes two additional positioning networktopologies:

-   -   1) using an antenna array coupled with a positioning-unit device        to form a remote beam pointing at a positioning receiver, which        receives the signal using a simple omni-directional antenna; and    -   2) using antenna arrays coupled to both the positioning-unit        device and the positioning receiver to produce a “composite”        beam as shown in FIG. 3.

In some embodiments, these two additional topologies are combined toprovide a scalable positioning system. For example, when the positioningreceiver is to be integrated into a portable device, such as a cellularor mobile telephone, it can make use of a simple omni-directionalantenna, provided that the positioning-unit device is coupled with anantenna array configured to form beams in accordance with the presentinvention. When a more accurate positioning solution is required or inenvironments where the positioning-unit device is not equipped with asuitable antenna array, an external antenna array can be configured asan add-on to the portable device for positioning applications. Suchexternal antenna arrays can be made with varying sizes depending on theaccuracy of the positioning solution required and in consideration ofthe size and type of antenna array coupled with the positioning-unitdevices in the positioning network.

The tightness of the beam is proportional to the number of elements and,therefore, the physical size of the antenna array. Therefore, it followsthat if the antenna array coupled with the positioning-unit device islarge, then the antenna array coupled with the positioning receiver maybe proportionately smaller and vice versa.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms.

In the claims below and the description herein, any one of the terms“comprising”, “comprised of”, or “which comprises” is an open term thatmeans including at least the elements/features that follow, but notexcluding others. Thus, the term “comprising”, when used in the claims,should not be interpreted as being limitative to the means or elementsor steps listed thereafter. For example, the scope of the expression adevice comprising A and B should not be limited to devices consistingonly of elements A and B. Any one of the terms “including”, “whichincludes”, or “that includes” as used herein is also an open term thatalso means including at least the elements/features that follow theterm, but not excluding others. Thus, “including” is synonymous with andmeans the same as “comprising”.

The claims defining the invention are as follows:

1. A device for remotely forming a beam at antenna arrays, the deviceincluding: an antenna array having a plurality of spatially distributedelements; a positioning-unit device coupled with said antenna array,said positioning-unit device configured to switch said antenna elementsbetween first and second states in a predetermined sequence wherein, insaid first state, said elements are configured to transmit a positioningsignal; and a receiver configured to receive said positioning signalfrom said antenna array, said receiver having a processor for generatinga reference signal, mixing said positioning signal with a modifiedreference signal to generate a mixed signal and summing the mixed signalover a predetermined integration period to generate an accumulatedsignal, wherein said reference signal is modified prior to being mixedwith said received signal such that said accumulated signal isindicative of the direction and magnitude of the beam of the antennaarray.
 2. A device according to claim 1 wherein said receiver includesat least one receive channel having a correlator, wherein saidcorrelator is configured to selectively manipulate the phase and/or gainof said reference signal in substantial synchronisation with saidpredetermined sequence.
 3. A device according to claim 2 wherein saidpositioning signal includes a pseudorandom code having a unique chipsequence within a predefined chip period, said unique chip sequencebeing used to provide said substantial synchronisation.
 4. A deviceaccording to claim 3 wherein said predetermined integration period isdivided into a number of sub-integration periods wherein each of saidelements are switched to said first state for the duration of saidsub-integration period.
 5. A device according to claim 4 wherein theswitching of each said element to said first state is aligned to a chipboundary within said unique chip sequence, wherein said sub-integrationperiod is synchronised to begin at the same time as said chip boundaryin the next chip period.
 6. A device according to claim 4 wherein eachsub-integration period is configured to access a respective accumulatorfor storing said positioning signal, wherein each said respectiveaccumulator is mixed with said modified reference signal to generatesaid mixed signal.
 7. A device according to claim 4 wherein the durationof each sub-integration period within said predetermined integrationperiod is dynamically adjustable such that the positioning signaltransmitted from one or more elements are selectively excluded frombeing mixed with said reference signal.
 8. A device according to claim 2wherein the manipulation of said phase and/or gain is achieved byrespectively applying a phase and/or gain offset to said referencesignal, wherein the value of said phase and/or gain offset is calculatedin dependence upon said predetermined sequence.
 9. A device according toclaim 2 wherein said correlator includes a carrier numerical controloscillator (NCO) and said reference signal is synthesised in saidcarrier NCO.
 10. A device according to claim 8 wherein the value of saidphase and/or gain offset is calculated by said processor in real time.11. A device according to claim 8 wherein the value of said phase and/orgain offset is calculated in advance and stored in a database that isavailable for retrieval by said processor.
 12. A device according toclaim 1 wherein in said first state, said element is active and in saidsecond state, said element is inactive.
 13. A device according to claim1 wherein said antenna elements are spatially distributed in a threedimensional configuration such that the device can form beams in one ormore dimensions.
 14. A device according to claim 1 wherein each receiverincludes multiple receive channels, wherein each receive channel isadaptable to form at least one beam.
 15. A device according to claim 1wherein elements switched to the second state are configured to benon-resonant such that the effects of mutual-coupling are ameliorated.18. A device for remotely forming a beam at an antenna arrays, thedevice including: an antenna array having a plurality of spatiallydistributed elements; a positioning-unit device coupled with saidantenna array, said positioning-unit device configured to a) switch saidantenna elements between first and second states in a predeterminedsequence wherein, in said first state, said elements are configured totransmit a modified positioning signal; and b) synthesise a positioningsignal and modify said positioning signal, in substantial synchronismwith said predetermined sequence, to generate a modified positioningsignal; and a receiver configured to receive said modified positioningsignal from said antenna array, said receiver having a processor forgenerating a reference signal, mixing said modified positioning signalwith said reference signal to generate a mixed signal and summing themixed signal over a predetermined period to generate an accumulatedsignal such that said accumulated signal is indicative of the directionand magnitude of the beam of the antenna array.
 19. A system for formingcomposite beams between antenna arrays, the system including: a transmitantenna array having a plurality of spatially distributed elements, saidtransmit antenna array being coupled to a positioning-unit device thatis configured to switch said antenna elements between first and secondstates in a predetermined sequence wherein, in said first state, saidelements are configured to transmit a positioning signal; a receiveantenna array having a plurality of spatially distributed elements, saidreceive antenna array being coupled to a positioning receiver that isconfigured to switch said antenna elements between first and secondstates in a predetermined sequence wherein, in said first state, saidelements are configured to receive a positioning signal; and saidpositioning receiver having a processor configured to: receive saidpositioning signal from said transmit antenna array, synthesize areference signal: modify said reference signal in substantialsynchronism with the switching of said elements of said transmit andreceive antenna arrays to the first state to generate a modifiedreference signal; mix said positioning signal with said modifiedreference signal to generate a mixed signal; and sum the mixed signalover a predetermined period to generate an accumulated signal such thatsaid accumulated signal is indicative of the direction and magnitude ofsaid beam of said transmit and receive antenna arrays.
 20. A method forforming a beam at antenna arrays, the method including the steps of: a)switching, at a positioning-unit device, spatially distributed elementsof said antenna array from a second state to a first state in apredetermined sequence, wherein, in said first state, said elements areconfigured to transmit a positioning signal; b) receiving, at areceiver, a positioning signal; c) generating, in a correlator of thereceiver, a reference signal for correlation with said positioningsignal; d) applying, in substantial synchronisation with receiving saidpositioning signals, a predetermined offset to said reference signal tocreate a modified reference signal; e) mixing said positioning signalwith said modified reference signal to create a mixed signal; and f)accumulating said mixed signal over an integration period to create anaccumulated signal, wherein said accumulated signal is indicative of thedirection and magnitude of said beam of said antenna array.
 20. A methodfor forming composite beams between antenna arrays, the method includingthe steps of: a) switching, at a positioning-unit device, spatiallydistributed elements of a transmit antenna array from a second state toa first state in a predetermined sequence, wherein, in said first state,said elements are configured to transmit a positioning signal; b)switching, at a positioning receiver, spatially distributed elements ofa receive antenna array from a second state to a first state in apredetermined sequence, wherein, in said first state, said elements areconfigured to receive a positioning signal; c) receiving, at apositioning receiver, a positioning signal; d) generating, in acorrelator of said positioning receiver, a reference signal forcorrelation with said positioning signal; e) modifying said referencesignal in substantial synchronism with the switching of said elements ofsaid transmit and receive antenna arrays to the first state to generatea modified reference signal; f) mixing said positioning signal with saidmodified reference signal to create a mixed signal; and g) accumulatingsaid mixed signal over an integration period to create an accumulatedsignal, wherein said accumulated signal is indicative of the directionand magnitude of said beam of said transmit and receive antenna arrays.21. A method for forming a beam at antenna arrays, the method includingthe steps of: a) synthesising, in a positioning-unit device, apositioning signal; b) switching, at a positioning-unit device,spatially distributed elements of said antenna array from a second stateto a first state in a predetermined sequence, wherein, in said firststate, said elements are configured to transmit a modified positioningsignal; c) applying, in substantial synchronisation with the switchingof one of said elements to the first state, a predetermined offset tosaid positioning signal to create said modified positioning signal; d)receiving, at a receiver, said modified positioning signal; e)generating, in a correlator of the receiver, a reference signal forcorrelation with said modified positioning signal; f) mixing saidmodified positioning signal with said reference signal to create a mixedsignal; and g) accumulating said mixed signal over an integration periodto create an accumulated signal, wherein said accumulated signal isindicative of the direction and magnitude of said beam of said antennaarray.